hexagonal-architecture

# Hexagonal Architecture ## Package Structure ``` src/main/java/com/example/ ├── domain/ ← Pure Java. Zero framework dependencies. │ ├── model/ ← Entities, value objects, aggregates │ ├── port/ │ │ ├── in/ ← Use case interfaces (driving ports) │ │ └── out/ ← Repository/external interfaces (driven ports) │ └── service/ ← Domain services (pure business logic) ├── application/ ← Orchestrates use cases. Spring allowed here. │ └── usecase/ ← @Service implementations of domain ports └── infrastructure/ ← All framework/DB/HTTP details ├── persistence/ ← JPA adapters implementing out ports ├── web/ ← REST controllers (driving adapters) └── external/ ← HTTP clients, messaging adapters ``` ## Domain Layer — Zero Spring ```java // domain/model/Order.java — pure Java, no annotations public class Order { private final OrderId id; private final CustomerId customerId; private OrderStatus status; private final List<OrderItem> items; private Order(OrderId id, CustomerId customerId) { this.id = id; this.customerId = customerId; this.status = OrderStatus.PENDING; this.items = new ArrayList<>(); } public static Order create(CustomerId customerId) { return new Order(OrderId.generate(), customerId); } public void addItem(P...